Essentially what you can do is add an identifier for each ‘tab’ and then save it in a multidimensional array, this is a neat trick that inputs can do and works great for WordPress plugins that uses tabs.
<form id="form_1">
<div class="tab_1">
<input type="text" name="tab1['fieldname_0']" value="tab_1_0">
<input type="text" name="tab1['fieldname_1']" value="tab_1_1">
<input type="text" name="tab1['fieldname_2']" value="tab_1_2">
<input type="text" name="tab1['fieldname_3']" value="tab_1_3">
</div>
<div class="tab_2">
<input type="text" name="tab2['fieldname_0']" value="tab_2_0">
<input type="text" name="tab2['fieldname_1']" value="tab_2_1">
<input type="text" name="tab2['fieldname_2']" value="tab_2_2">
<input type="text" name="tab2['fieldname_3']" value="tab_2_3">
</div>
</form>
Your PHP wont need to change, but your return data when calling get_option() will change to an array which is easy to iterate over from there or reference by $key.